Screen angle calculation

Support
1

Hi Chris,

Last week I was setting up mWorks in a new setup and to verify I had gotten all the screen size and distance measurements correctly, I measured the size of a 10 degree stimulus on the screen and after doing some trigonometry, I discovered it was actually being displayed at an 11 degree size. I double checked all my measurements and my math and I am fairly sure they are correct. I was wondering if you might be able to tell me what assumptions/equations mWorks makes when computing the size to display a stimulus (for example, does it assume a spherical screen?) or if you have any other thoughts on what else could cause this oddity.

Thanks,

Simon

2

Hi Simon,

There’s a pretty detailed description of how MWorks computes the bounds of the screen in degrees of visual angle in another discussion. It doesn’t make any assumptions about the shape of the screen, but it does assume there’s enough distance between the screen and the subject for the small angle approximation to be valid.

Cheers,
Chris